Method and apparatus for hierarchical picture encoding and decoding

ABSTRACT

A residual picture is decoded first by demultiplexing an input enhancement layer bitstream into one or more bitstreams corresponding to an order of quality layers. Next, a residual picture is restored by independently decoding the bitstream for each quality layer. The restored residual picture is stored in a frame buffer. A finally restored residual picture is output by adding, to the restored residual picture, a picture that has undergone motion compensation in a reference frame within a same enhancement layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(a) of U.S. Provisional Application No. 61/382,594, filed in the United States Patent and Trademark Office on Sep. 14, 2010, which is incorporated by reference, herein, in its entirety.

FIELD

The inventive concept relates generally to hierarchical (or layered) picture encoding/decoding technology and, more particularly, to a hierarchical picture encoding/decoding method and apparatus for refining picture quality using residual pictures in video compression codec processing videos.

BACKGROUND

Generally, in video compression technology, pictures (or images) are processed in units of macro blocks having M×N pixels per block. In video processing, macro blocks are encoded and decoded in either an intra mode or an inter mode. The term ‘macro block,’ as used herein, may be understood to refer to a set of pixel blocks that each have a specific size. A ‘frame’ includes multiple macro blocks. The typical video compression technology using macro blocks may include the use of compression standards such as MPEG and H.26x.

The basic concept of video compression is to remove spatially and temporally redundant data from the original picture data. The intra mode is a scheme for removing spatial redundancy. In other words, this mode is a scheme for removing redundancy, between pixels in macro blocks having a specific size, in the current frame. The inter mode is a scheme for removing temporal redundancy. In other words, this mode is a scheme for estimating a difference between macro blocks of a current frame and corresponding macro blocks of a previous or of a following frame (referred to as a “reference” frame) by estimating motions between corresponding macro blocks in the two adjacent frames. The motion estimation is a process of searching for macro blocks in the reference frame, which are similar to macro blocks to be encoded in the current frame. In picture encoding, motion compensation is performed using the macro blocks in the reference frame, which were searched for by the motion estimation process and were found. A picture encoder entropy-encodes a difference between the “found” macro blocks in the reference frame and macro blocks in the current frame, along with a motion vector representing the location of the reference frame during its transmission.

Typically, in motion compensation, a residual encoder/decoder calculates multiple residual differential pictures for the multiple quality layers constituting its input residual picture, and also performs motion compensation on the residual differential pictures independently, causing an increase in its complexity and encoding/decoding time.

SUMMARY

An aspect of the exemplary embodiments is to provide a method and apparatus for reducing complexity and refining picture quality during picture encoding, especially during residual encoding in hierarchical picture processing technology.

Another aspect of the exemplary embodiments is to provide a method and apparatus for reducing complexity and refining picture quality during picture decoding, especially during residual decoding in hierarchical picture processing technology.

In accordance with one exemplary embodiment, a residual picture of picture data in hierarchical picture processing is encoded, and this includes a basement layer and at least one enhancement layer. Also, a picture of the enhancement layer is divided into one or more quality layers. The method includes combining the residual picture with a picture that has already undergone motion compensation in a reference frame within a same enhancement layer. A bitstream is generated for each quality layer by encoding the combined picture independently for each quality layer. Residual differential pictures generated in the process of encoding the combined picture are stored, in associated frame buffers, independently for each quality layer. A motion-compensated picture is output by selectively performing motion compensation on the pictures stored in the frame buffers; and outputting an enhancement layer bitstream by multiplexing the bitstreams for the individual quality layers.

In accordance with another exemplary embodiment, an apparatus encodes a residual picture of picture data in hierarchical picture processing. In the apparatus, one picture includes a basement layer and at least one enhancement layer. A picture of the enhancement layer is divided into one or more quality layers. The apparatus includes a quality layer encoder for combining the residual picture with a picture that has already undergone motion compensation, in a reference frame within the same enhancement layer. The encoder also generates a bitstream and a residual differential picture for each quality layer. It does this by encoding the combined picture independently for each quality layer. The apparatus also has a frame buffer for storing the residual differential pictures generated by the quality layer encoder. The apparatus also has a motion compensator for outputting a motion-compensated picture by selectively performing motion compensation on the pictures stored in the frame buffer. Additionally, there is a multiplexer for outputting an enhancement layer bitstream by multiplexing the bitstreams for the individual quality layers.

In accordance with further exemplary embodiment, there is provided a method for decoding a residual picture of picture data, in hierarchical picture processing, in which one picture includes a basement layer and at least one enhancement layer. Also, a picture of the enhancement layer is divided into one or more quality layers. The method includes demultiplexing an input enhancement layer bitstream into one or more bitstreams. The bitstreams correspond to an order of the quality layers. In this method, a residual picture is restored by decoding the bitstream independently for each quality layer. The restored residual picture is stored in a frame buffer. The finally restored residual picture is output by adding to the restored residual picture a picture that has undergone motion compensation in a reference frame within the same enhancement layer.

In accordance with yet another exemplary embodiment, an apparatus decodes a residual picture of picture data in hierarchical picture processing in which one picture includes a basement layer and at least one enhancement layer, and a picture of the enhancement layer is divided into one or more quality layers. The apparatus includes a demultiplexer for demultiplexing an input enhancement layer bitstream into one or more bitstreams corresponding to an order of the quality layers. The apparatus also includes a quality layer decoder for restoring a residual picture by decoding the bitstream for each the quality layer independently. A frame buffer stores the residual picture that was restored in the equality layer decoder. A motion compensator outputs the finally restored residual picture by adding, to the restored residual picture, a picture that has undergone motion compensation in a reference frame within the same enhancement layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of certain exemplary embodiments will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a structure of a hierarchical picture encoder;

FIG. 2 illustrates a structure of a hierarchical picture decoder;

FIG. 3 illustrates a structure of a residual encoder according to an exemplary embodiment;

FIG. 4 illustrates a structure of a quality layer encoder according to an exemplary embodiment;

FIG. 5 illustrates a structure of a selective motion compensator according to an exemplary embodiment;

FIG. 6 illustrates a structure of a residual encoder according to another exemplary embodiment;

FIG. 7 illustrates a structure of a residual decoder in a hierarchical picture decoder according to an exemplary embodiment;

FIG. 8 illustrates a structure of a residual decoder in a hierarchical picture decoder according to another exemplary embodiment;

FIG. 9 illustrates a residual encoding process according to an exemplary embodiment; and

FIG. 10 illustrates a residual decoding process according to an exemplary embodiment.

DETAILED DESCRIPTION

Exemplary embodiments will now be described in detail, with reference to the accompanying drawings. In the following description, specific details (such as detailed configuration and particular components) are provided merely to assist the overall understanding of the exemplary embodiments. Therefore, it should be apparent to those skilled in the art that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the inventive concept. In addition, descriptions of well-known functions and constructions have been omitted for clarity and conciseness, and to avoid obscuring the inventive concept.

The inventive concept includes, among others, a method and apparatus for performing residual encoding and/or decoding on multiple quality layers, constituting an enhancement layer bitstream/picture in a hierarchical picture encoding/decoding process.

First, the terms used herein will be defined, in brief, as follows.

Quality refinement: a process for refining the quality of residual samples reconstructed using refined data.

Quality layers: one or more layers used in the quality refinement process.

Quality basement layer: a layer representing the lowest-quality picture among reconstructed pictures, among multiple quality layers in one picture.

Quality enhancement layer: a layer representing a high-quality picture among reconstructed pictures, among multiple quality layers in one picture.

A general hierarchical picture encoding/decoding apparatus will now be described.

FIG. 1 illustrates the structure of a hierarchical picture encoder.

Referring to FIG. 1, the picture encoder operates according to a hierarchical structure including a basement layer and one or more enhancement layers, accepts an input picture for encoding, and outputs a basement layer bitstream and an enhancement layer bitstream. A picture of the basement layer and a picture of the enhancement layer may be pictures having different resolutions, sizes and/or view points.

It is assumed, in the example of FIG. 1, that the input picture and the picture processed in the enhancement layer are high resolution pictures, are pictures having a large size, and/or are pictures representing one view point. It is also assumed that the picture processed in the basement layer is a low resolution picture, a picture having a small size, and/or a picture representing another view point. A format down-converter 101 down-converts the input picture into a picture having a format the same as that of the basement layer. For example, the down-converter 101 performs a down-conversion in terms of the size (or frame rate) of the input picture or a view point of a stereoscopic picture. A basement layer encoder 103 outputs a basement layer bitstream generated by encoding the input basement layer picture according to an existing encoding scheme using, e.g., video codecs such as VC-1, H.264, MPEG-4 Part 2 Visual, MPEG-2 Part 2 Video, AVS, and JPEG2000. In the process of encoding the basement layer picture, the basement layer encoder 103 outputs a basement layer picture reconstructed to a format up-converter 105.

The format up-converter 105 is configured to perform an up-conversion in terms of, for example, the size (or the frame rate) or a view point of an input picture, and may be considered to perform a process that is a reverse of the process of the format down-converter 101. The format up-converter 105 up-converts the reconstructed basement layer picture into a picture having the same format as that of the enhancement layer. The input picture that is input to the format down-converter 101 is also input to a subtractor 107. The subtractor 107 outputs residual data obtained by subtracting the up-converted picture, output by format up-converter 105, from the input picture. A residual mapping/scaling unit 109 converts the residual data into a residual picture. The residual picture is input to residual encoder 111, which outputs an enhancement layer bitstream by performing residual encoding on the input residual picture.

A method for encoding a residual picture to gradually refine the quality in one enhancement layer will now be described.

The residual encoder 111 includes a quality layer encoder (not shown) and a motion compensator (not shown). The quality layer encoder performs encoding on quality layers independently so as to encode the residual picture in multiple quality layers.

FIG. 2 illustrates the structure of a hierarchical picture decoder.

Referring to FIG. 2, the picture decoder operates according to a hierarchical structure including a basement layer and one or more enhancement layers, and outputs a reconstructed basement layer picture and a reconstructed enhancement layer picture. It does this by decoding the basement layer bitstream and the enhancement layer bitstream which were respectively encoded by the picture encoder in FIG. 1. The picture of the basement layer and the picture of the enhancement layer may be pictures having different resolutions, sizes and/or view points.

It is assumed, in the example of FIG. 2, that the input picture and the picture processed in the enhancement layer are high resolution pictures, are pictures having a large size, and/or are pictures representing one view point. It is also assumed that the picture processed in the basement layer is a low resolution picture, a picture having a small size, and/or a picture representing another view point. A basement layer decoder 201 outputs a reconstructed basement layer picture. It does this by decoding the input basement layer bitstream according to a decoding scheme that corresponds to the video codec that was used in the basement layer encoder 103 in FIG. 1. The basement layer picture that is reconstructed by the basement layer decoder 201 is itself output, and is also outputted to a format up-converter 203. The format up-converter 203 up-converts the reconstructed basement layer picture into a picture that is the same format as the enhancement layer. A residual decoder 205 inputs the enhancement layer bitstream, and outputs a residual picture. This residual picture is generated by carrying out residual decoding on the input enhancement layer bitstream. The residual picture is next converted into residual data by a residual mapping/scaling unit 207. The residual data is next added to the format up-converted picture by an adder 209, and the result is the generation of a reconstructed enhancement layer picture.

The residual decoder 205 includes a quality layer decoder (not shown) and a motion compensator. The quality layer decoder performs decoding on the quality layers independently so as to reconstruct the residual picture in multiple quality layers.

FIG. 3 illustrates the structure of a residual encoder according to an exemplary embodiment. Although the residual encoder in FIG. 3 has three quality layers, this is merely for the sake of providing a teaching example; the number of quality layers is subject to change.

Referring to FIG. 3, the residual encoder includes three quality layer encoders 301, 303 and 305, the number of which corresponds to the number of quality layers. The residual encoder also includes a selective motion compensator 307.

A residual picture input to the residual encoder is encoded into a first bitstream and a first residual differential picture by the first quality layer encoder 301. The second quality layer encoder 303 encodes a picture, corresponding to a difference between the residual picture and the first residual differential picture, into a second bitstream and a second residual differential picture. The third quality layer encoder 305 encodes a picture, corresponding to a difference between the residual picture and the second residual differential picture, into a third bitstream and a third residual differential picture. The first to third residual differential pictures are inputs of the selective motion compensator 307. The selective motion compensator 307 carries out motion compensation, depending on a motion vector, and outputs a motion-compensated picture. A picture corresponding to a difference between the residual picture and the motion-compensated picture is input back to the first quality layer encoder 301. The first to third bitstreams are integrated (or multiplexed) into one bitstream (i.e., an enhancement layer bitstream) by a multiplexer (not shown), and then transmitted to a decoder over a transport channel.

FIG. 4 illustrates the structure of a quality layer encoder according to an exemplary embodiment.

Referring to FIG. 4, the quality layer encoder includes a transform encoder 401, a quantizer 403, a variable-length encoder 405, a de-quantizer 407, and an inverse-transform encoder 409. The transform encoder 401 calculates a transform coefficient by transform-encoding a differential picture received from a quality layer encoder on an N×N block basis. The quantizer 403 quantizes the transform coefficient for an N×N block, and the variable-length encoder 405 generates a bitstream from the quantized level values. The level values quantized by the quantizer 403 restore the transform coefficient by means of the de-quantizer 407. The inverse-transform encoder 409 outputs a reconstructed differential picture. It does this by restoring the picture, which is accomplished by performing inverse-transform for the restored coefficient value.

In order to achieve gradual quality refinement for a residual picture, as for residual differential pictures reconstructed by the quality layer encoders in FIG. 3, the quality of the residual picture is progressively refined from the first differential picture on to the third differential picture. The quality layer encoder in FIG. 4 may achieve such a gradual quality refinement by adjusting a quantization parameter of the quantizer 403. For example, the quality layer encoder may restore a differential picture whose quality is gradually refined by progressively reducing the quantization parameter of the quantizer 403 in order of the first quality layer to the third quality layer.

FIG. 5 illustrates the structure of a selective motion compensator according to an exemplary embodiment. Although the selective motion compensator in FIG. 5 has three quality layers, this is merely for the sake of providing a teaching example; the number of quality layers is subject to change.

Referring to FIG. 5, the selective motion compensator includes three frame buffers 501, 503 and 505, the number of which corresponds to the number of quality layers, and a motion compensator 507. The residual differential pictures, restored by their associated quality layer encoders, are added to the motion-compensated picture output from motion compensator 507. Then they are stored in their associated frame buffers 501, 503 and 505. The restored residual pictures stored in the frame buffers 501, 503 and 505 are selectively input to the motion compensator 507 under control of the encoder, and used for motion compensation. The encoder transmits, in a header, information indicating with which frame buffer it has performed motion compensation, so that a decoder can subsequently perform the same operation.

FIG. 6 illustrates a structure of a residual encoder according to another exemplary embodiment. Although the residual encoder in FIG. 6 has three quality layers, this is merely for the sake of providing a teaching example; the number of quality layers is subject to change.

Referring to FIG. 6, quality layer encoders 601, 603 and 605 for the quality layers may use the structure illustrated in FIGS. 3 and 4, except that only the residual differential pictures output from the first quality layer encoder 601 for the first quality layer, and the third quality layer encoder 603 for the last quality layer, are stored in first and third frame buffers 607 and 609, respectively, and they are all used for motion compensation of a motion compensator 611. In a residual encoder with multiple quality layers, frame buffers are always provided only for reconstructed differential pictures of the lowest quality layer and the highest quality layer. In other words, in FIG. 6, the residual encoder with two or more quality layers always has just two frame buffers, regardless of the number of quality layers.

FIG. 7 illustrates the structure of a residual decoder in a hierarchical picture decoder according to an exemplary embodiment. Although the residual decoder in FIG. 7 has three quality layers, this is merely for the sake of providing a teaching example; the number of quality layers is subject to change.

Referring to FIG. 7, first to third bitstreams (or enhancement layer bitstreams being input to the residual decoder) are input to corresponding first to third quality layer decoders 710, 720 and 730 for their associated quality layers. The first to third quality layer decoders 710, 720 and 730 include variable-length decoders 711, 721 and 731, de-quantizers 713, 723 and 733, and inverse-transform encoders 715, 725 and 735, respectively.

The first bitstream is converted, in the first variable-length decoder 711, into quantized level values using variable-length decoding. Next, it is converted into a transform coefficient for an N×N block, in the first de-quantizer 713, using a de-quantization operation. The transform coefficient is inverse-transformed on an N×N block basis, in the first inverse-transform encoder 715, and then added to a motion-compensated picture from motion compensator 740. The result is stored in a first frame buffer 750.

The second bitstream is converted, in the second variable-length decoder 721, into quantized level values using variable-length decoding Next, it is converted into a transform coefficient for an N×N block , in the second de-quantizer 723, using a de-quantization operation. The transform coefficient is inverse-transformed on an N×N block basis, in the second inverse-transform encoder 725, and then added to the sum of the picture restored in the first quality layer decoder 710 and the motion-compensated picture from motion compensator 740. The result is delivered to the third quality layer decoder 730.

The third bitstream is converted, in the third variable-length decoder 731, into quantized level values using variable-length decoding. Next, it is converted into a transform coefficient for an N×N block, in the third de-quantizer 733, using a de-quantization operation. The transform coefficient is inverse-transform encoded on an N×N block basis in the third inverse-transform encoder 735, and then added to a sum of the pictures restored in the first and second quality layer decoders 710 and 720 and of the motion-compensated picture from motion compensator 740. The result is stored in a third frame buffer 760 The picture stored in the third frame buffer 760 is output as a residual picture finally restored in the residual decoder.

The pictures stored in the first and third frame buffers 750 and 760 are used for motion compensation in the motion compensator 740.

FIG. 8 illustrates the structure of a residual decoder of a hierarchical picture decoder according to another exemplary embodiment. Although the residual decoder in FIG. 8 has three quality layers, this is merely by way of example, and the number of quality layers is subject to change.

Referring to FIG. 8, first to third quality layer decoders 810, 820 and 830 are substantially the same as those in FIG. 7, in terms of the structure and operation, except for an operation of output stages of the first to third quality layer decoders 810, 820 and 830. In other words, a picture output from a first inverse-transform encoder 815 in the first quality layer decoder 810 is stored intact in a first frame buffer 850; a picture output from a second inverse-transform encoder 825 in the second quality layer decoder 820 is added to the picture output from the first inverse-transform encoder 815, and delivered to the third quality layer decoder 830. A picture output from a third inverse-transform encoder 835 in the third quality layer decoder 830 is added to a sum of the picture output from the second quality layer decoder 820 and the motion-compensated picture from a motion compensator 840, and the result is stored in a third frame buffer 860. The picture stored in the third frame buffer 860 is output as a residual picture finally restored in the residual decoder.

In other words, when the quality refinement between pictures is applied in the hierarchical picture decoder as in the exemplary embodiment, a residual block is restored by adding a motion-compensated block to an inverse-transform encoded block in a quality basement layer (or a first quality layer), and the restored residual samples constitute a picture of the quality basement layer. In addition, inverse-transform blocks of quality enhancement layers (e.g., second and third quality layers in FIGS. 7 and 8) connected to the quality basement layer are used to refine the quality of a inverse-transform block of the quality basement layer. The inverse-transform block whose quality was finally refined is added to the motion-compensated picture in the motion compensator. After the quality refinement process, the quality enhancement layer picture is restored by the restored residual samples.

FIG. 9 illustrates a residual encoding process according to an exemplary embodiment.

Referring to FIG. 9, when a residual picture is input to a residual encoder in step 901, the residual picture is added to a picture that has undergone motion compensation in a reference frame within the same enhancement layer, and then input to quality layer encoders in step 903. In step 905, bitstreams are independently generated for quality layers in their associated quality layer encoders, and residual pictures are restored and stored in frame buffers. A residual picture restored in a high quality layer encoder is used to generate a bitstream in the next lower quality layer encoder. Frame buffers may be provided either for all quality layers, or for only the highest and lowest quality layers. In step 907, the pictures stored in the frame buffers undergo motion compensation, and then are used for generating bitstreams of the next frame. In accordance with an exemplary embodiment, one of the pictures stored in all frame buffers may selectively undergo motion compensation. Alternatively, both of the pictures stored in the frame buffers corresponding to the highest and the lowest quality layers may undergo motion compensation. In step 909, the bitstreams generated in their associated quality layer encoders are multiplexed into one enhancement layer bitstream, and then transmitted to a decoder.

FIG. 10 illustrates a residual decoding process according to an exemplary embodiment.

Referring to FIG. 10, in step 1001, an enhancement layer bitstream input to a residual decoder is demultiplexed into multiple bitstreams, the number of which corresponds to the number of quality layers. In step 1003, residual pictures for individual quality layers are restored by independently decoding the demultiplexed bitstreams for the quality layers by means of quality layer encoders. In step 1005, the restored residual pictures for individual quality layers are stored in associated frame buffers for restoration of residual pictures of the next frame, and then undergo motion compensation. In step 1007, the finally restored residual picture is output by adding the motion-compensated picture of a reference frame within the same enhancement layer to the restored residual pictures for individual quality layers. The restored residual pictures are reconstructed as an enhancement layer picture by being combined with the basement layer picture. In accordance with an exemplary embodiment, when the finally restored residual picture is made by combining the residual pictures independently restored for quality layers, the picture that has undergone motion compensation in the highest quality layer decoding process may be reflected, or the picture that has undergone motion compensation in the lowest quality layer decoding process may be reflected. In the quality layer decoders, the restored residual pictures are used for restoring a residual picture in a high quality layer decoder.

As is apparent from the foregoing description, according to the exemplary embodiments, multiple residual pictures have to undergo motion compensation only once, thus ensuring a lower-complexity residual encoder/decoder.

According to the exemplary embodiments, the drift occurs not in the original picture but in the residual picture, and this reduces the degradation in picture quality due to drift, and thereby ensures effective, scalable encoding.

While the inventive concept has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventive concept as defined by the appended claims and their equivalents. 

What is claimed is:
 1. A method for encoding a residual picture of picture data in hierarchical picture processing in which one picture includes a basement layer and one or more enhancement layers, and in which a picture of the enhancement layer is divided into one or more quality layers, comprising: combining the residual picture with a picture that has undergone motion compensation in a reference frame within a same enhancement layer, and generating a bitstream for each quality layer by independently encoding the combined picture for each quality layer; storing, in associated frame buffers, residual differential pictures generated in the process of independently encoding the combined picture for each quality layer; outputting a motion-compensated picture by performing motion compensation on the pictures stored in the frame buffers; and outputting one enhancement layer bitstream by multiplexing together the bitstreams for the individual quality layers.
 2. The method of claim 1, wherein: a picture corresponding to a difference, between (1) a picture obtained by combining the residual picture with the picture that has undergone motion compensation in the reference frame, and (2) a residual differential picture generated in a process of encoding a picture for a low quality layer is used as an input signal in an encoding process for each quality layer.
 3. The method of claim 1, wherein the storing comprises storing, in associated frame buffers, residual differential pictures generated in an encoding process of a highest one of the one or more quality layers and a lowest one of the one or more quality layers.
 4. The method of claim 3, wherein the outputting of a motion-compensated picture comprises outputting the motion-compensated picture by performing motion compensation on all of the residual differential pictures generated in the encoding process of the highest one of the one or more quality layers and the lowest one of the one or more quality layers.
 5. An apparatus for encoding a residual picture of picture data in hierarchical picture processing in which one picture includes a basement layer and one or more enhancement layers, and in which a picture of the enhancement layer is divided into one or more quality layers, comprising: a quality layer encoder adapted to combine the residual picture with a picture that has undergone motion compensation in a reference frame within a same enhancement layer, and adapted to generate a bitstream and a residual differential picture for each quality layer by independently encoding the combined picture for each quality layer; a frame buffer adapted to store residual differential pictures generated in the quality layer encoder; a motion compensator adapted to output a motion-compensated picture by performing motion compensation on the pictures stored in the frame buffer; and a multiplexer adapted to output a single enhancement layer bitstream by multiplexing the bitstreams for the individual quality layers.
 6. The apparatus of claim 5, wherein the quality layer encoder uses, as an input signal, a picture corresponding to a difference between: (1) a picture obtained by combining the residual picture with the picture that has undergone motion compensation in the reference frame, and (2) a residual differential picture generated in a process of encoding a picture for a lower quality layer.
 7. The apparatus of claim 5, wherein the frame buffer stores residual differential pictures generated in an encoding process of a highest one of the one or more quality layers and a lowest one of the one or more quality layers.
 8. The apparatus of claim 7, wherein the motion compensator outputs the motion-compensated picture by performing motion compensation on all of residual differential pictures generated in the encoding process of the highest one of the one or more quality layers and the lowest one of the one or more quality layers.
 9. A method for decoding a residual picture of picture data in hierarchical picture processing in which one picture includes a basement layer and one or more enhancement layers, and in which a picture of the enhancement layer is divided into one or more quality layers, comprising: demultiplexing an input enhancement layer bitstream into one or more bitstreams corresponding to an order of the one or more quality layers; restoring a residual picture by decoding the bitstream for each quality layer independently, and storing the restored residual picture in a frame buffer; and outputting a finally restored residual picture by adding a picture, that has undergone motion compensation in a reference frame within a same enhancement layer, to the restored residual picture.
 10. The method of claim 9, wherein the outputting of a finally restored residual picture comprises outputting a finally restored residual picture by adding (1) a picture that has undergone motion compensation in a reference frame within a same enhancement layer, to (2) a picture obtained by adding up residual pictures restored in each quality layer decoding process.
 11. The method of claim 9, wherein the storing comprises: storing in a first frame buffer a picture obtained by adding (1) the picture that has undergone motion compensation in the reference frame to (2) a residual picture restored in a lowest quality layer decoding process, the first frame buffer corresponding to a lowest one of the one or more quality layers; and storing the finally restored residual picture in a second buffer corresponding to a highest one of the one or more quality layer.
 12. The method of claim 11, wherein the picture stored in at least one of the first and second frame buffers is used to restore a residual picture of a next frame after undergoing motion compensation.
 13. The method of claim 9, wherein the storing comprises: storing a residual picture restored in a lowest quality layer decoding process, in a first frame buffer corresponding to the lowest one of the one or more quality layers; and outputting a picture obtained by adding (1) the picture that has undergone motion compensation in the reference frame to (2) the residual picture restored in a highest quality layer decoding process, as the finally restored residual picture, and storing the finally restored residual picture in a second frame buffer corresponding to a highest one of the one or more quality layers.
 14. The method of claim 13, wherein the picture stored in at least one of the first and second frame buffers is used to restore a residual picture of a next frame after undergoing motion compensation.
 15. An apparatus for decoding a residual picture of picture data in hierarchical picture processing in which one picture includes a basement layer and one or more enhancement layers, and in which a picture of the enhancement layer is divided into one or more quality layers, comprising: a demultiplexer adapted to demultiplex an input enhancement layer bitstream into one or more bitstreams corresponding to an order of the one or more quality layers; a quality layer decoder adapted to restore a residual picture by independently decoding the bitstream for each quality layer; a frame buffer storing the residual picture restored in the quality layer decoder; and a motion compensator adapted to output a finally restored residual picture by adding (1) a picture that has undergone motion compensation in a reference frame within a same enhancement layer, to (2) the restored residual picture.
 16. The apparatus of claim 15, wherein the motion compensator outputs a finally restored residual picture by adding (1) a picture that has undergone motion compensation in a reference frame within a same enhancement layer, to (2) a picture obtained by adding up residual pictures restored in each decoding process of the one or more quality layers.
 17. The apparatus of claim 15, wherein the frame buffer comprises: a first frame buffer storing a picture obtained by adding (1) the picture that has undergone motion compensation in the reference frame to (2) a residual picture restored in a lowest quality layer decoder; and a second frame buffer storing the finally restored residual picture.
 18. The apparatus of claim 17, wherein the motion compensator performs motion compensation on the picture stored in at least one of the first and second frame buffers, and uses the motion-compensated picture to restore a residual picture of a next frame.
 19. The apparatus of claim 15, wherein the frame buffer comprises: a first frame buffer storing a residual picture restored in a lowest quality layer decoder; and a second frame buffer storing, as the finally restored residual picture, a picture obtained by adding (1) the picture that has undergone motion compensation in the reference frame to (2) the residual picture restored in a highest quality layer decoder.
 20. The apparatus of claim 19, wherein the motion compensator performs motion compensation on the picture stored in at least one of the first and second frame buffers, and uses the motion-compensated picture to restore a residual picture of a next frame.
 21. A residual encoder, comprising: a plurality of sequenced quality layer encoders, including at least a first quality layer encoder and a last quality layer encoder; a selective motion compensator that outputs a motion-compensated picture; wherein: the first quality layer encoder generates a first residual differential picture based on a difference between a residual picture and the motion-compensated picture, the first residual differential picture being output to the selective motion compensator and to a subsequent one of the plurality of sequenced quality layer encoders; each subsequent one of the plurality of sequenced quality layer encoders generates a respective residual differential picture based on a difference between the residual picture and the picture output by an immediately preceding one of the plurality of sequenced quality layer encoders, the respective residual differential picture being output to the selective motion compensator and to another subsequent one of the plurality of sequenced quality layer encoders; and the last quality layer encoder generates a last residual differential picture based on a difference between a residual picture and the respective residual differential picture received from the immediately preceding one of the plurality of sequenced quality layer encoders, the last residual differential picture being output to the selective motion compensator.
 22. The residual encoder as set forth in claim 21, further comprising frame buffers storing only the first and the last residual differential pictures.
 23. The residual encoder as set forth in claim 21, further comprising frame buffers storing a respective residual differential picture corresponding to each of the plurality of sequenced quality layer encoders. 